Modification of polyurethane foams with zinc sulfide nanoparticles and their novel composites with multani mitti and charcoal for oil spill cleanup

With the rapid growth of the automobile industry, the excessive number of industrial pollutants, particularly oil spills, has become a huge threat to the natural environment. Therefore, an environmentally benign and sustainable solution is required for an effective oil spill cleanup. To enhance the sorption capacity of pristine polyurethane (PU) foam used in oil spill cleanup, ZnS nanoparticles were deposited on PU foam via a coprecipitation approach. Additionally, the effect of Fuller's earth, locally known as Multani Mitti (MM), and charcoal (CC) on the sorption properties of the PU foam were investigated and compared. Polyvinyl alcohol (PVA) was used as a binder during the modification procedure. The morphology, chemical composition, and thermal stability of ZnS/MM/PVA- and ZnS/CC/PVA-modified PU sorbents were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and X-ray photon spectroscopy (XPS). The modified PU foam exhibited outstanding properties including a high sorption capacity, high selectivity to different types of used oils such as vegetable oil, hydraulic oil, lube oil, and gear oil, and superior reusability in comparison to pristine PU foam. ZnS/CC/PVA has a sorption capacity of 16.78 g g−1 while ZnS/MM/PVA exhibited a sorption capacity of 16 g g−1. In addition, after 10 cycles of oil sorption-squeezing experiments, the oil sorption capacity remained unchanged, and the absorbed used oil could be removed and collected by an easy squeezing procedure prior to reuse. This work reveals that the ZnS/CC/PVA- and ZnS/MM/PVA-modified PU foams have a promising potential for oil spill removal and environmental protection.


Introduction
Accidental release of liquid petroleum hydrocarbons into the environment, usually through water, is known as an oil spill.Oil spills, becoming an everyday incident, attract signicant media and official attention when they are of signicant scale or occur in environmentally vulnerable areas.The petroleum from oil elds to consumers necessitates delivery through various means of transportation, including tankers, pipelines, railcars, and tank trucks.Petroleum is kept at many locations, including transfer sites, terminals, and reneries situated along its transportation path.Accidents have the potential to occur at several stages of manufacture, transit, or storage. 1,2l spills are an environmental threat that can be attributed to the extensive utilization of oil and petroleum derivatives.Globally, an estimated 20 million tons are used on a daily basis. 3orous polymeric composites are regarded as highly efficient adsorption materials due to their ease of preparation and recyclability, such as polypropylene (PP)/polyester (PET) bre, 4 polyacrylonitrile (PAN)/reduced graphene oxide (rGO), 5 and waste newspaper/waste polystyrene (PS). 6][9][10] Various polymer grades have been utilized as oil adsorbents, including foams, 11,12 resins, 13,14 sponges, 15 and aerogels. 16,17olyurethane foams have garnered signicant interest in recent times for their application in oil/water separation processes 18,19 within the eld of various polymer matrices.Nevertheless, the inclusion of polar groups, such as carboxyl and amino groups, inside the PU frameworks makes these materials hydrophilic, hence affecting their selectivity and overall performance.PU foams, which include characteristics such as ultralight, open-cell structure, high porosity, and low density have been well recognized for their effectiveness as oil sorbents. 20Extensive studies have been conducted on the impact of the cell structure 21 and foam density on the oil sorption capabilities of PU. 22 Insufficient emphasis has been placed on the surface modication of PU foams with the objective of enhancing their oleophilic/hydrophobic properties for the purpose of oil spill remediation. 18A PU foam-based adsorbent for oil spill cleanup has been reported by Wu et al., which was prepared through a novel method by treating PU foam with SiO 2 .The volume of the PU foam was 13.5 cm 3 .The sorption capacities of motor oil and diesel oil were 103 and 95 g g −1 , respectively. 19inc sulde (ZnS) is an n-type semiconductor that has a broad band gap (2.6-4.6 eV), strong electrical mobility, good thermal stability, non-toxicity, water insolubility, large surface area, and is relatively inexpensive.ZnS has been identied as a suitable nanomaterial for the removal of organic contaminants from wastewater. 23uller's earth (MM) is commonly used in subcontinent South Asia for cleansing skin and has been employed in various applications, owing to its notable adsorption capabilities and costeffectiveness. 24Bleaching earth enhances the oil's quality and lightens the tone of any coloured oil by modifying the basic colour units in the oil without changing the chemical qualities of the oil.Additionally, it eliminates other impurities such as soap, aromatic compounds, residual metals, oxidized substances, and phospholipids. 24,25Charcoal/activated carbon (CC) covers a diverse array of amorphous carbon-based substances that are characterized by their high porosity and extensive interparticulate surface areas. 26By increasing the adsorbent quantity and contact time, oil removal is improved by CC.With a removal efficiency of 99.67%, CC was determined to be the most effective adsorbent compared to rice hull. 27CC can be modied to acquire magnetic properties to facilitate cleanup collection. 28,29lyvinyl alcohol (PVA) is a linear or semi-crystalline synthetic polymer that is white or creamy in colour, tasteless and odourless, nontoxic, biocompatible, and thermostable. 30,31t has been used as a binder in this work to improve the adherence of deposited lms.
This work presents a simple, effective, and innovative approach that involves the utilization of PU foam derived from discarded laboratory materials as a sorbent for oil spills.To the best of our knowledge, ZnS/CC/PVA and ZnS/MM/PVA-modied PU foams were employed for the rst time to improve the oil sorption capacity.The presence of ZnS effectively improved the oil adsorption capacity.The modied PU foam was characterized by FT-IR, SEM, TGA and XPS.Several used oils were adopted as model pollutants, and the sorption mechanism was identied.The modied PU foams can continuously, quickly and effectively separate the used oil from water.It also has an important feature for large-scale applications in oil spill cleanup.
Synthesis of the ZnS/CC/PVA-modied PU foam.The PU foam was washed by an immersion process, which includes acetone and deionized (DI) water solution in an ultrasonic bath for 15 minutes.Subsequently, the foam was dried in an oven at a temperature of 60 °C for 2 hours.
Modication of PU foams by ZnS/CC/PVA was carried out via coprecipitation method.The PU foam was coated with ZnS nanoparticles using 1 M Zn(NO 3 ) 2 $6H 2 O and 2 M Na 2 S in the presence of TX-100 at 60 °C.Aer 2 h, the calculated amount of CC powder and PVA were added to the solution with continuous stirring for 3 h.Finally, ZnS/CC/PVA-modied PU foams and the resulting precipitates were collected and dried at 50 °C for 24 h in an oven, as shown in Fig. 1.The CC powder was used by wt%, i.e., 0.03 wt%, 0.06 wt%, 0.09 wt%, 0.12 wt%, and 0.15 wt% of ZnS, and the series of modied PU foams were prepared with the sample names of CC3, CC6.CC9, CC12 and CC15, respectively.
Synthesis of ZnS/MM/PVA modied PU foam.The PU foam was washed by an immersion process, which included acetone and DI water solution in an ultrasonic bath for a duration of 15 minutes.Subsequently, the foam was dried in an oven at a temperature of 60 °C for 2 hours.
Modication of PU foams by ZnS/MM/PVA was carried out using the same procedure as mentioned above for ZnS/CC/PVA, and the series of modied PU foams were prepared with the sample names of MM3, MM6.MM9, MM12 and MM15.
The ZnS nanoparticles interacted with the PU foam.During deposition, hydrogen bonds were formed between ZnS and PU foam.The remaining void spaces were lled with the CC and MM, and PVA was added for the binding of ZnS, CC, and MM.The overall mechanism of the ZnS/CC/PVA and ZnS/MM/PVA-modied PU foams is shown in Fig. 2.

X-ray diffraction (XRD)
The XRD patterns of CC and MM were obtained by a Bruker D8 Advance X-ray diffractometer with a Cu Ka radiation wavelength (l) of 1.5418 Å within the 2q range of 5-70°.The Bragg equation was utilized to determine the spacing (d) between the diffracting planes of CC and MM: where d is the interplanar distance, q denotes the scattering angle, n is a positive integer, and l is the wavelength of X-rays.
The crystallite size was calculated using the Scherrer equation.
where b denotes the full-width at half-maximum (FWHM), and l is the wavelength of the X-rays. 32eld emission scanning electron microscopy (FE-SEM) The modied PU foam structure was observed by ZEISS FE-SEM at 15 kV with an Oxford energy-dispersive X-ray spectrometer (EDS) for elemental analysis.

Fourier transform infrared spectroscopy (FT-IR)
Fourier Transform Infrared Spectroscopy (FT-IR) measurements were performed using attenuated total reectance (ATR) by a Bruker TENSOR 27.The spectra were measured at 4000-600 cm −1 and the wavenumber revolution was 4 cm −1 .

Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC)
TGA of ZnS/MM/PVA and ZnS/CC/PVA were performed in a nitrogen environment by METLLER Toledo TGA with a sample Paper RSC Advances weight of 3.827 mg, and within the temperature range of 49-900 °C.

X-ray photoelectron spectroscopy (XPS)
The XPS data were acquired using a Scienta-Omicron system that was tted with a micro-focused monochromatic Al K-alpha X-ray source.The data collection was done using Matrix soware, while the subsequent data analysis was carried out with CasaXPS soware, using XPS t techniques.The process of tting the detailed spectra involved the utilization of Gaussian-Lorentzian line shape aer background adjustments.

Density
The densities of the pristine PU foam, ZnS/CC/PVA and ZnS/ MM/PVA-modied PU foams were obtained by calculating the weight and volume of each respective foam sample.The samples were weighed using a high-precision analytical balance (with a readability of 0.0001 g), and their size was measured using a scale.Each group utilized different samples to determine the density (r).The density was computed using the following equation: 33 where m, l, w, and h are the weight, length, width, and height of the samples, respectively.

Measurement of the oil sorption performance
The oil and other solvent absorption capacities of the adsorbent were determined.Before immersion in the liquids, the adsorbent sample mass was measured and observed.Aer saturation, the foam was removed and allowed to drain freely until dripping stopped.It was then placed in a pre-weighed container, and weighed and recorded.The sorption capacity (S c ) was determined using the following equation: where m i and m t are the weights of the PU foam before and aer the rst absorption, respectively.

Reusability
The reusability of the adsorbent was determined by measuring the change in the weight of the adsorbent aer compressing the absorbed oils and the quantity of recovered oils.This process was performed 10 times.The oil recovery rate (R%) is calculated as follows: where m n is the weight of the recovered oil at the nth time.All tests were performed at room temperature. 34sults and discussions XRD XRD analysis was used to investigate the crystallographic information of the CC and MM, as shown in Fig. 3. XRD analysis showed the monoclinic crystal system of CC and orthorhombic system for MM. 35The diffraction peaks at 20.99°, 26.79°, and 42.66°, which correspond to the (102), (111), and (204) crystal planes, respectively, are similar to the diffraction peaks of the monoclinic crystal system of CC (JCPDS 96-590-0036).In addition, the peaks at 19.9034°, 26.7382°, 34.8477°, and 50.2705°Fig.

FE-SEM
The SEM images of the pristine PU foam are shown in Fig. 4.
The surface modication of the PU foam with the ZnS/CC/PVA nanocomposite was analysed with FESEM/EDX before the sorption test.These foams possess void spaces and surface areas to absorb the used oil.The surface modication of the PU foam with the ZnS/MM/ PVA nanocomposite was observed with FESEM/EDX before the sorption test.These foams possess a void space and surface area to absorb the used oil.Fig. 8a and b compares the morphology of the nanocomposite before and aer the oil sorption test.We observed that aer surface modication, the surface becomes rough due to the coating of ZnS/MM/PVA.Due to amplication or enlargement of the solid-liquid interactions, this introduced irregularity to the foam inuences its interaction with a wetting or nonwetting liquid.The uniform cell structure and spherical shape of the modied foam sorbent indicate that the incorporation of ZnS/MM/PVA into the foam did not result in the destruction of the PU foam structure. 36Fig. 8a shows that the modied PU foam has ZnS, MM and PVA.Fig. 8b shows that aer 10 cycles of the oil sorption test, the surface stability of the PU foam is quite evident.

FT-IR
The FT-IR spectra of the CC3, CC6, CC9, CC12, and CC15-modied PU foams are shown in Fig. 11.The observed wide absorption peaks at 3510.9 cm −1 for the modied PU foam are caused by the O-H bond stretching vibrations of PVA.The broadness of the band peak decreases when the quantity of CC increased. 37The peaks found at 2041 cm −1 are due to the presence of CO 2 molecules from the atmosphere. 38The presence of the functional group as the double bond C]C indicates the existence of the aromatic stretching vibration at 1627.9 cm −1 . 39The peak seen at 1390.7 cm −1 corresponds to the carboxyl (C]O) and methylene groups. 38The peak observed at 1058.1 cm −1 is caused by the existence of the C-O functional group, specically the stretching of C-O bonds in the acetyl groups.The peak is shied towards the le when the quantity of CC increased. 40he FT-IR spectra of the MM3, MM6, MM9, MM12, and MM15-modied PU foams are shown in Fig. 12.The observed wide absorption peaks at 3428.6 cm −1 for the modied PU foam are caused by O-H bonds of the stretching vibrations of water, and the broadness of the band peak decrease when the quantity of MM increased. 37The band at 2758.3 cm −1 indicated the carboxyl acid. 41In addition, a peak at around 2422.4 cm −1 was assigned to the C]O stretching vibrations. 42When the quantity of MM increased, the peaks at 2758.3 cm −1 , 2422.2 cm −1 and 2076 cm −1 disappeared.The presence of the C]C double bond is indicated by the existence of the aromatic stretching vibration at 1633.9 cm −1 . 39The peak seen at 1405.7 cm −1 corresponds to the C-H bending vibration of CH 2 . 40,43The band peak at

Viscosity of used oil
The viscosities of the commercial and used oils at 25 °C and 40 °C temperature are shown in Table 1.

TGA
Thermal stability of the ZnS/CC/PVA composite was evaluated using TGA, as shown in Fig. 13.The composite material demonstrated a three-stage decomposition process, leading to three distinct phases of weight reduction when subjected to a nitrogen environment.The rst degradation stage was detected in the temperature range between 214-295 °C, and the corresponding weight losses for the composite samples were observed to be 1.2%.The observed decline can be attributed to the process of moisture evaporation, and is related to the water loss. 51The second degradation happened within the temperature range of 295-370 °C, having weight losses of 4.5%.This degradation is attributed to the decomposition temperature of the PVA structure. 52,53The maximum degradation happened at the third phase within the temperature range of 370-481 °C, resulting in a weight loss of 13.1% that represents the ash and xed carbon content. 51The nal weight of the sample is 80.14%.
The differential scanning calorimetry (DSC) analysis associated with the TGA of ZnS/CC/PVA exhibited the heat ow change with temperature, and was used to determine the melting and crystallization temperatures.The melting 54 and crystallization 55 temperatures of the composite were evaluated as 322 °C and 465 °C, respectively.
Thermal stability of the ZnS/MM/PVA composite was evaluated using TGA, as shown in Fig. 14.The composite material demonstrated a three-stage decomposition process, leading to three distinct phases of weight reduction when subjected to a nitrogen environment.The rst degradation stage was detected within the temperature range of 59-279 °C, and the corresponding weight losses for the composite samples were observed to be 2.5%.The observed decline can be attributed to the process of moisture evaporation and related to the water loss. 51The maximum degradation happened at the second phase within the temperature range of 279-551 °C, having weight losses of 40.3%.The second degradation is caused by the elimination of water molecules that were strongly attached to the octahedral cations, as well as the removal of silanol groups     Paper RSC Advances from MM 56 and the thermal decomposition of the precursor into ZnS particles. 57This degradation is attributed to the decomposition temperature of the PVA structure. 52,53The third phase degradation occurs within the temperature range of 551-804 °C, resulting in a weight loss of 5.1%.This weight loss can be ascribed to the emission of CO 2 as a result of decomposition. 58The nal weight of the sample is 50.91%.The differential scanning calorimetry (DSC) analysis associated with the TGA of ZnS/MM/PVA exhibited the heat ow change with temperature, and was used to determine the melting and crystallization temperatures.The melting 54 and crystallization 55 temperatures of the composite were evaluated as 321 °C and 411 °C, respectively.

XPS
The survey spectra of the ZnS/CC/PVA-modied PU foam composites are displayed in Fig. 15a.Particularly, the peaks corresponding to Zn 2p 3/2 , O 1s, C 1s, and S 2p are readily Table 3 Oil sorption capacity (g g −1 ) of the ZnS/MM/PVA-modified PU foam Pump/hydraulic (g g −1 ) Engine/lube (g g −1 ) Gear (g g  discernible.The binding energy of Zn 2p 3/2 observed at 1020.5 eV indicates the presence of Zn 2+ in ZnS. 59The 1022.0 eV binding energy of Zn 2p 3/2 can be attributed to the Zn-S bond 60 (Fig. 15b).The S 2p peaks at 160 eV, 160.4 eV and 161.7 eV can be attributed to the S bond in ZnS (S-) shown in Fig. 15c. 61The composites' high-resolution C 1s XPS spectrum is illustrated in Fig. 15d.The peaks indicated the existence of C-C bonds at about 283.2 eV and C-O-C bonds at around 284.9 eV, which both correlate to the accumulation of the carbon content on the surface of the coating.A low-intensity wide peak, indicative of carboxylate bonds, was found at around 286.3 eV. 62The peak at 530 eV indicated the presence of substances that collected on the surface of the coating. 62The O 1s peak had the highest intensity at the binding energy of 531.6 eV, corresponding to C]O, 63 in comparison to the other elements shown in Fig. 15e.The broad peak is composed of the OH group of PVA.Due to the large number of -OH groups in PVA, the O 1s intensity was the highest. 64The peak at 532.8 eV corresponds to the C-O-C/C-OH bond. 63

Density
The densities of the PU foam are directly related with its absorption capacity, 33 and calculated by eqn (3).The initial density of the pristine PU foam is 0.05 g cm −3 .However, the density of the foam rises to 1.94 g cm −3 and 0.16 g cm −3 when increasing concentrations of CC and MM were added.This indicates the good adherence of ZnS/CC/PVA and ZnS/MM/PVA to the surface of the PU foam by the process of dip coating.

Sorption test
Used oils (such as vegetable oil, hydraulic oil, gear oil and lube oil) are used for the oil sorption test.Firstly, we measured the ZnS, ZnS/PVA-modied PU foams for comparison.The sorption capacities of the pristine PU foam in vegetable oil, hydraulic oil, gear oil and lube oil are 3.2, 2.5, 2.1 and 1.9 g g −1 , respectively.The sorption capacities of ZnS in vegetable oil, hydraulic oil, gear oil and lube oil are 7.82, 6.91, 5.39, and 6.65 g g −1 , respectively.The sorption capacities of ZnS/PVA in vegetable oil, hydraulic oil, gear oil and lube oil are 9.25, 7.23, 6.10, and 8.24 g g −1 , respectively.The sorption capacities of CC in vegetable oil, hydraulic oil, gear oil and lube oil are 7.7, 6.19, 7.75 and 6.5 g g −1 , respectively.The sorption capacities of CC/PVA in vegetable oil, hydraulic oil, gear oil and lube oil are 10.2, 10.5, 9, and 9.3 g g −1 , respectively.The sorption capacities of ZnS/CC in vegetable oil, hydraulic oil, gear oil and lube oil are 7.8, 6.61, 8, and 8.6 g g −1 , respectively.These sorption capacities of pristine PU foam, ZnS, ZnS/PVA, CC, CC/PVA and ZnS/CC-modied PU foam are compared in Table 2 and Table 3.Now, we dip the ZnS/CC/PVA-modied PU foam into the oil water solution, and then drip it for approximately two minutes, as shown in Fig. 16.The modied PU foam has greatly improved oil sorption capacity, as shown in ESI Videos (V1-V4).† The ZnS/ CC/PVA-modied PU foam has excellent sorption capability, and can easily adsorb oil droplets above or below the water surface (when the foam was dipped under water).When oil is adsorbed in the modied PU foam pores, the pore volume of the PU foams was completely lled and also adsorbed on the outer surface of the foam.Its absorption capacities vary with the usage of different oils.The sorption capacity of the modied PU foams is shown in Table 2. CC9 has the high sorption capacity compared to the other modied foams, which is calculated by eqn (4).The sorption capacity graph of the modied PU foam is shown in Fig. 17.
The modied PU foam has greatly improved oil sorption capacity, as shown in the ESI Video.† The ZnS/MM/PVA-modied PU foam has excellent sorption capability, and can easily absorb oil droplets above or below the water surface (when the foam was dipped under water by tweezers).When oil is adsorbed in the modied PU foam pores, the pore volume of the PU foams was completely lled and also adsorbed on the    3. MM12 has the high sorption capacity compared to the other modied foams, which is calculated by eqn (3).The sorption capacity graph of the modied PU foam is shown in Fig. 18.The MM is more adhesive than CC, and the surface area of CC is greater than that of MM. 65 This is why the sorption capacity of MM is less than that of CC.

Reusability
The ZnS/CC/PVA and ZnS/MM/PVA-modied PU foams have good elasticity, and the oil can be easily removed by soly squeezing the foam (Fig. 19 and 20).However, the PU foam does not completely remove all of the oil when it is squeezed.Aer the absorption or desorption cycle, a small portion of the nanocomposite was detached from the modied PU foam, but this does not decrease the oil absorption ability.The recovery rate of the vegetable, hydraulic, lube, and gear oils was 73%, 68%, 70% and 67%, respectively, by the ZnS/CC/PVA-modied PU foam.The recovery rate of the vegetable, hydraulic, lube, and gear oils was 71%, 66%, 79% and 63%, respectively, by the ZnS/MM/PVA-modied PU foam.Table 4 shows the comparative study with the previous literature.

Mechanical stability
The weight capacity of the PU foam increased as a result of the coating with ZnS/CC/PVA and ZnS/MM/PVA nanocomposites.The ZnS/CC/PVA and ZnS/MM/PVA-modied PU foams have exceptional mechanical durability.Thus, when putting a 600 g weight onto a pristine PU foam with dimensions of 2 cm × 2 cm × 1 cm, the sponge exhibited signicant compression and deformation.In contrast, the ZnS/CC/PVA and ZnS/MM/PVA modied PU foams exhibited remarkable mechanical strength, enabling it to retain its original shape even under the same weight load (shown in Fig. 21).The mechanical strength of the ZnS/CC/PVA and ZnS/ MM/PVA-modied PU foams exhibits different characteristics. 68

Conclusions
In this study, ZnS/CC/PVA and ZnS/MM/PVA were used to improve the oil sorption capacity of the PU foam.The ZnS/CC/ PVA and ZnS/MM/PVA-modied PU foams with different concentrations of CC and MM were modied by coprecipitation method for oil spill cleanup.XRD, FESEM, FTIR, TGA and XPS conrm the successful preparation of the ZnS/CC/PVA and ZnS/ MM/PVA-modied PU foams.Used oils (such as vegetable, lube, hydraulic and gear oils with different viscosities) were selected for the sorption capacity test.The ZnS/CC/PVA and ZnS/MM/PVA-modied PU foams have exceptional mechanical strength and high sorption capacity, absorbing gear oil that is 16.78 and 16 times its own weight, respectively.Aer that, it can be reused 10 times by squeezing.Its sorption capacity remains essentially the same.Furthermore, it possesses excellent cyclic stability and reusability.The experimental results demonstrated that the ZnS/ CC/PVA and ZnS/MM/PVA-modied PU foam sorbents hold great promise for oil spill cleanup and recovery in oil-water systems.

Fig. 5
Fig. 5 (a) SEM image of the ZnS/CC/PVA-modified PU foam before the oil sorption test.(b) SEM image of the ZnS/CC/PVA-modified PU foam after oil sorption.
Fig. 6 SEM image of the ZnS/CC/PVA-modified PU foam; (a and b) EDX mapping and elemental analysis, including elemental analysis of (c) Zn, (d) S, (e) O, and (f) C before the oil sorption test.

Fig. 7
Fig. 7 SEM image of the ZnS/CC/PVA-modified PU foam; (a and b) EDX mapping and elemental analysis, including elemental analysis of (c) Zn, (d) S, (e) O, and (f) C after the oil sorption test.

Fig. 9
shows the results of the elemental mapping before the oil sorption test, which indicate the presence of Zn, S, C, O, Si and Al, suggesting that the ZnS/MM/PVA nanoparticles are present.Throughout the nanocomposite, Zn, S, C, O, Si and Al atoms were found to be evenly dispersed.The results of the oil sorption test, as depicted in Fig.10, revealed the presence of Zn, S, C, O, Si, and Al using elemental mapping.This suggests the existence of the ZnS/MM/PVA nanoparticles.The nanocomposite exhibited a uniform dispersion of Zn, S, C, O, Si, and Al atoms throughout the material.The carbon content was increased aer conducting an oil sorption test.

Fig. 8
Fig. 8 (a) SEM image of the ZnS/MM/PVA-modified PU foam before the oil sorption test.(b) SEM image of the ZnS/MM/PVA-modified PU foam after the oil sorption test.

Fig. 9
Fig. 9 SEM image of the ZnS/MM/PVA-modified PU foam; (a and b) EDX mapping and elemental analysis, including elemental analysis of (c) Zn, (d) S, (e) O, (f) C, (g) Al, and (h) Si before the oil sorption test.

Fig. 10
Fig. 10 SEM image of the ZnS/MM/PVA-modified PU foam; (a and b) EDX mapping and elemental analysis, including elemental analysis of (c) Zn, (d) S, (e) O, (f) C, (g) Al, and (h) Si after the oil sorption test.
Fig. 17 Sorption capacity graph of the ZnS/CC/PVA-modified PU foam.

Table 1
Viscosity of the used oil measured at room temperature